1. Field of the Invention
The invention relates to differential pressure indicators.
2. Brief Review of the Prior Art
Differential pressure indicators are used to provide an indication, such as a visual indication or an electrical signal, when the difference between two fluid pressures exceeds a predetermined value. This is often achieved by applying the pressures to opposite sides of a piston which moves from an inoperative position to an operative position when the predetermined value is reached.
In one known indicator of this kind, the piston carries a rod which moves from a non-visible position to a visible position as the piston moves from the inoperative position to the operative position. The rod thus provides a visual indication that the predetermined pressure differential has been exceeded.
Such indicators are used, for example, in filters to indicate the onset of clogging of the filter element which increases the pressure differential upstream and downstream of the filter in the fluid being filtered.